Understand the rule first
Identify the scale and units before using the data. Mean is total ÷ number of values; range is largest − smallest.
Read data carefully and calculate mean, range and comparisons from the correct values.
Identify the scale and units before using the data. Mean is total ÷ number of values; range is largest − smallest.
Dividing by the largest value instead of by the number of values when finding a mean.
Reusable method: Check whether a graph scale increases in ones, twos, fives or another interval.Subtract the smallest value from the largest.
Answer C: 12
21 − 9 = 12.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Reverse total ÷ number by multiplying.
Answer D: 72
Total = mean × number of scores = 18 × 4 = 72.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Add the four values and divide by four.
Answer C: 12
7 + 11 + 12 + 18 = 48; 48 ÷ 4 = 12.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Find the required total, then subtract the four known values.
Answer B: 15
Required total = 5 × 16 = 80. Known total = 65. The missing number is 15.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
The distance from a negative minimum to a positive maximum crosses zero.
Answer D: 12°C
9 − (−3) = 12°C.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Add all five values, then divide by five.
Answer C: 10
The total is 50; 50 ÷ 5 = 10.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Subtract the smallest value from the largest.
Answer D: 12
19 − 7 = 12.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Put the values in order first.
Answer A: 8
In order they are 3, 7, 8, 12, 14. The middle value is 8.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Find the difference in grid squares before applying the scale.
Answer B: 16 pupils
The bars differ by 4 squares; 4 × 4 pupils = 16 pupils.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.
Use the original mean to find the original total.
Answer C: 16.5
The original total is 5 × 18 = 90. Removing 24 leaves 66; 66 ÷ 4 = 16.5.
Quick method: Check whether a graph scale increases in ones, twos, fives or another interval.